Beer is supposed to be pretty simple.

Water, malt, hops and yeast, right?

But fish guts?

Yeah, things just got weird.

For centuries brewers have used something called isinglass to help turn cloudy beer clear. And isinglass comes from one of the last places most beer drinkers would expect: the swim bladders of fish.

Which inevitably led to the considerably more entertaining description, “fish guts in your beer.”

But that’s not entirely accurate.

Isinglass is actually a highly processed form of collagen derived from fish swim bladders, internal organs that fish use to control their buoyancy in the water. Historically, sturgeon was prized as a source of isinglass, although commercial brewing products today are generally made using tropical fish.

And brewers aren’t adding the stuff to influence a beer’s taste.

They’re adding it because isinglass is remarkably effective at making beer clear.

After fermentation, yeast and other tiny particles can remain suspended in beer, giving it a cloudy appearance. Isinglass acts as what brewers call a fining agent, attracting suspended yeast cells and causing them to clump together into larger masses that eventually settle toward the bottom.

And the end result is the kind of bright, clear beer that drinkers traditionally expected, particularly with British cask ales, where isinglass has played an important role for generations.

But that brings us back to the whole “fish guts in your beer” thing.

Isinglass is considered a processing aid. It does its work by helping yeast and other suspended material settle out of the beer, with the finings remaining behind with the sediment rather than being poured into your glass.

So no, there aren’t chunks of fish bladder floating around in your pint.

But there’s still a catch.

Because isinglass comes from fish, beer produced using it isn’t considered vegan, even though the substance is used during production rather than as a conventional beer ingredient.

For years that created an interesting problem for one of the world’s most famous beers.

Guinness historically used isinglass as part of its clarification process. But as veganism grew and drinkers became increasingly interested in exactly what went into making their beer, fish-derived finings became harder to ignore.

Eventually Guinness changed the way it made its beer.

The Dublin brewer introduced a new filtration process that eliminated the use of isinglass, and today Guinness Draught, Guinness Extra Stout and Guinness Foreign Extra Stout are considered vegan-friendly.

Guinness isn’t alone in finding other ways to get the job done.

Brewers now have a number of alternatives available to them, including silica-based finings and products derived from carrageenan, commonly associated with Irish moss. Modern centrifuges and filtration systems can also help remove suspended material without relying on fish-derived collagen.

And then craft beer came along and made things even more interesting.

For generations, clarity was considered a sign of a properly made beer. Cloudiness could suggest that something had gone wrong, so brewers went to considerable lengths to produce a pint that arrived brilliantly clear.

Today?

Some beer drinkers practically demand the haze.

The rise of Hazy and New England IPAs radically changed expectations about what beer is supposed to look like. Wheat, oats, proteins, hop compounds and suspended yeast can all contribute to that cloudy appearance, and in many modern beer styles haze isn’t something brewers are desperately trying to eliminate.

It’s part of the attraction.

Which is pretty funny when you think about it.

Brewers spent centuries perfecting ways to make cloudy beer clear, including figuring out that processed fish swim bladders were exceptionally good at doing it.

Then along came craft beer drinkers who looked at a glass of beer resembling orange juice and said, “We’ll have that.”

But isinglass hasn’t disappeared.

It remains particularly associated with traditional British cask ale, where beer continues conditioning in the cask and sediment can be disturbed during transportation and handling. Isinglass helps that yeast settle again, allowing the beer to “drop bright” before it’s served.

And for brewers who still use it, there’s a simple reason why this centuries-old technique survives.

It works.

There are plenty of strange ingredients that have found their way into beer over the centuries, but few come with a backstory quite as unlikely as isinglass.

So the next time somebody tells you there are fish guts in their beer, you can correct them.

They’re not fish guts.

They’re processed fish swim bladders used to make the beer clearer.

Which, now that we think about it, really doesn’t sound much better.

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And while we’re at it there’s this…

5 Weird Beers To Avoid Like The Plague